Pushbutton switch



March 18, 1,969 E- R- ERICSSON 3,433,914

PusHBu'rToN SWITCH Filed Oct. 25. 1967 II'UIENTOP. R\L Rlbnb. E lmsso'BY QN.

TTQRNEYS United States Patent O 3,433,914 PUSHBUTTON SWITCH Eric R.Ericsson, Hagersten, Sweden, assignor to Telefonaktiebolaget L MEricsson, Stockholm, Sweden, a corporation of Sweden Filed Oct. 25,1967, Ser. No. 678,108 Claims priority, application Sweden, Feb. 24,1967,

2,633/ 67 U.S. CI. 200-159 Int. Cl. H01h 3/12, 3/14, 13/64 6 ClaimsABSTRACT F THE DISCLOSURE The present invention relates to a switchingdevice, especially suitable for application to printed circuit boards.Such switching devices comprising push button operating means are usedfor instance in pushbutton sets for pulsing in telephone instruments.These pushbutton sets which must be mounted in the space provided forthe conventional dial, must not be bulky, whereby the design of thedevice presents a problem, especially as the space available for therequired contact springs is limited.

A known design uses reed contacts that are located substantially inparallel relationship to thecircuit board and conveniently secured tothe same. When actuated, the movable springs make or break the contactwith fixed contacts provided on the board. In this arrangement, however,it becomes necessary to use short contact springs, which has inherentdisadvantages, such as a bad contact sliding at the closure moment ofcontact engagement, which may jeopardize an effective operation, as wellas cause a relatively high deflection stress on a short spring length.

In another known construction, reed springs of U-form are mounted on asupport projecting from the board, so that the arms of the U-formedsprings are placed perpendicularly to the board. 'By this arrangement anincreased spring length is obtained in comparison with thefirst-mentioned arrangement. The ends of the spring arms are insertedinto holes in the board to cooperate with fixed contacts arranged on theedges of the holes. Ihe spring movement is obtained by displacement ofthe push button in a direction tangential to the spring. In order toobtain the required magnitude of the movement of the contact it isnecessary to provide the spring with a deflection that is laterallydisplaced when pressing the button. This device, however, has thedisadvantage that the deflection of the contact spring might causefracture t of the spring.

The device of the invention is similar to this lastmentionedconstruction in that the springs are located on supports projectingvfrom the board and have contact arms that are substantiallyperpendicular to the board. It constitutes, however, an improvement ofthe known device in that the detlection length of the spring isconsiderably greater although the spring still occupies a reduced space.The spring furthermore is not subjected to bends that are likely tocause a fracture. These advantages are obtained by the contact springsbeing made of resilient 3 ,433 ,9 14 Patented Mar. 18, 1969 ICC wire andthe spring arm carrying the movable contact at an intermediate portionhaving a coil spiral of cylindrical form, the center axis of which isparallel to the plane of the board.

These and other advantages of the invention will be understood from thefollowing description that is made with reference to the attacheddrawing.

In the drawing FIGURE 1 shows an exploded view of the pushbuttonmechanism and FIGURE 2 shows the position of the contact spring in threedifferent phases of the pushbutton movement.

The pushbutton mechanism is supported by a base plate 1 of insulatingmaterial that may be common to a plurality of pushbuttons. The baseplate has secured thereon an elastic support 2 for each pushbuttonmechanism. A pushbutton 3 has a center shaft 4 that tits into a hole 5in the base plate 1, which hole serves as a guide for the shaft. As anadditional guiding means for the pushbutton 3 a cover plate 6 with asquare hole 7 is provided, through which hole the upper square portionof the pushbutton may protrude. To mount the mechanism, the shaft 4 isinserted into the hole 5, whereafter the cover plate 6 is placed overthe upper part of the pushbutton and in a convenient manner secured tothe base plate 1 at a predetermined distance from the same. For holdingthe buttonv in an inactive position the button is provided with ahelical spring 10, located on an upper part 8 of the center shaft, whichspring normally pushes the button 3 upwards, so that its flange 9 restsagainst the bottom side of the cover plate 6.

On the bottom side of the base plate a circuit board 11 with printed4circuits (not shown in the figure) is provided. The switching devicefurther comprises two movable contact `springs 13 and 14, one being amirror image of the other. The contact springs are made of resilientwire and designed to be mounted on the support 2. For this purpose theyare provided 'with a coil spiral 19 at their upper part, which coilspiral fits into a recess 21 in the support 2, where it is retainedwithout being squeezed. The recess 21 has an upper opening that issomewhat narrower than the outer diameter of the coil spiral. The coilspiral may, however, be pushed down through this opening because thesupport 2 is made of an elastic material.

`Each spring has at the end of one 'arm a cylindrical contact 17 forcooperation with a fixed contact '12. At an intermediate portion of thisarm is provided with a coil spiral 20 which partly serves to absorb thedeection stresses during the actuation of the spring and partly servesas an actuation surface for the pushbutton, thereby providing aconvenient trigger point as is explained below. The other arm of thespring is straight and, when mounting the spring in the support 2, thisarm is inserted into a hole 25 through the base plate 1 and the printedcircuit board 11, so that this arm may be soldered to a printed circuiton the bottom side of the circuit board as shown at 15 and 16 (FIG. 2).The cylindrical contact 17 provided on the end of the other arm isinserted into another hole 26. The fixed contact 12, made in form of awire, is located in a groove 27 in the bottom side of the base plate andhas a V-formed portion 18 for cooperation with the contact 17. The wire12 may at a convenient place cross the circuit board and be connected toa conductor on this board. a

The pushbutton is provided with an actuation member 23 for actuating thesprings. The actuation member is at its lower end provided with twosymmetrical curved recesses 24 for actuating the coil spirals 20 of thesprings 13 and 14. At the first moment of actuation the verticaldiameter of the coil spirals are practically in the same plane as thevertical side of the respective actuation member, a fact that producesthe desired trigger point effect (see FIG. 2). A person pressing thepushbutton has, in order to overcome the reaction of the spring, toincrease the force so that the springs are displaced laterally therebymaking contact with the fixed contacts. At the moment this occurs hecannot avoid pressing down the button to its lowermost position, wherebythe actuation member slides down between the coil spirals 20 Iof thecontact springs, the coil spirals resting against the side surfaces 28.By this trigger point etfect a minimum length of the spring movement isobtained.

I claim:

1. A switching device for switching conductors of a printed circuitboard, said switching device comprising in combination:

a printed circuit board mounting a support protruding from one side ofthe board;

a substantially V-shaped contact spring supported on said supportstraddling the same, one of the arms of the spring being connected toone of the conductors of the board and the other arm being switchableinto and out of contact with another conductor and biased into one ofits switching positions, said other arm having intermediate its length aspiral coil the center axis of which is substantially parallel to theplane of the board; and

an actuating member supported by said board on the side thereof mountingthe support and displaceable normal to the plane of the board, saidmember having on one end a portion engaging said spiral coil upondepressing the actuating member from an inactive position into apredetermined depressed position with reference to the plane of theboard, engagement of said portion with said spiral coil displacing thelatter substantially parallel to the plane of the board thereby exingsaid other spring arm into the other one of its switching positions andretaining said other arm in said other switching position.

2. The switching device according to claim 1 wherein said portion of theactuating member terminates in a curved taper, the curvature of saidtaper mating with the outside of said spiral coil in the inactiveposition of the actuating member, depression of the actuating memberinto said predetermined depressed position causing pressure engagementof said portion with the spiral coil thereby `snapping said otherspringarm into said other switching position.

3. The switching device according to claim 2 wherein the center axis ofsaid spiral coil and a at side wall of the actuating member portionengageable with the spiral coil are substantially disposed in a commonplane normal to the plane ofthe circuit board whereby an initialdepression of the actuating membercauses sliding of the curved tapersurface and the outer coil surface relative to each other and continueddepression of the actuating member causes a large and abrupt deflectionof said other spring arm in response to a small depression movement ofthe actuating member.

4. The device according to claim 1 wherein a pushbutton is secured tothe other end of the actuating member and a mounting post extends fromthe pushbutton into a hole of the board slidable therein, and wherein aspring is interposed between the board and the pushbutton biasing thelater into a position in which the actuating member is in said inactiveposition.

S. The device according to claim 1 wherein the arms of said V`shapedcontact spring are joined at the apex thereof by a second spiral coil,and wherein said support has at its upper end a recess, said second coilbeing received in said recess.

y6. The switching device according to claim 1 wherein said one arm ofthe contact spring is secured to a wire connected to said one conductorand including a V-shaped portion, said one end of the other spring armengaging both branches of said V-shaped portion in said other switchingposition of the other spring arm.

References Cited UNITED STATES PATENTS 7/ 1956 Fisher 20D-166.1 XR8/1958 Munn 20G- 166.8 XR

U.S. Cl. X.R.

